there actually are 123 CG spaces, if it was 0-123, it would have 124 spaces. think of it this way. if you have 5 spaces, it would be 0, 1, 2, 3, and 4. so 0-122 actually includes 122 spaces PLUS one, as zero is considered a number, last time i checked.
( i think ) you can only have CG's in one bank because if nintendo put them in every bank, the ROM would need expanded, and it wouldn't fit on a cartridge, plus, it would be pretty pointless to make a CG for your bedroom, and if you hacked a game, it would be pretty hard to replace ALL of them to match your cities.

hope i helped with your tut,

manyo

Thank you~My first reader~
Well,there are 122 pointers in that table ,but there are 123 maps.That is the problem.I was saying,why there're only 122 pointers,not 123.
Yes,you're right.And,I'm considering how the game judges the bank.
Anyway, thank you,really.